Spring supported scraper blade for the conduits of heat exchangers



y 1942 w G. VOGEL 2,282,298

SPRING SUPPORTED SCRAPER BLADE FOR CONDUITS OF HEAT EXCHANGERS OriginalFiled Oct. 26, 1938 BY EMMA 'BAR'TMAN VOGEL, EXECUTRIX.

Patented May 5, 1942 SPRING SUPPORTED SCRAPER BLADE FOR.

THE CONDUITS OF HEAT EXCHANGERS Werner G. Vogel, deceased, late ofLouisville, Ky.,

by Emma Ky.

Original application October 26,

Bartman Vogel, executrix, Louisville,

1938, Serial No.

237,135. Divided and this application Novemher 9, 1939, Serial No.303,709

3 Claims.

This invention relates to rotary scrapers for tubular heat exchangers,andparticularly those of the double pipe chiller type. Such generallycomprise a sinuous conduit consisting of a plur'ality of straight,substantially horizontal jacketed pipe sections serially connected atthe ends by return bends. The liquid to be chilled is pumped through theconduits while a refrigerant circulates through the jackets surroundingthe straight pipe sections.

This invention is a division of application Serial No. 237,135, filedOctober 26, 1938, upon which Patent No. 2,182,712 was granted onDecember 5, 1939.

It is well known that in the case of many liquids, such for example ashydrocarbon oils, chilling of the same precipitates out certain matters,the natural tendency of which is to collect upon the walls of theconduit in the form of an adherent sediment or scale, and if theconduits are left during off periods of operation filled with liquid,these matters frequently become persistently adherent and difficult toremove.

Now, in the interest of efficient heat exchange, it is essential notonly to keep the inner walls of the conduits free from deposits of thisnature, but also to maintain them in smooth and polished condition.

With this end in view, it is customary to mount driven scrapers in thestraight pipe sections of the chiller with ribbon blades arranged in thegeneral longitudinal direction, sometimes straight and sometimesspirally, which revolve against the inner surfaces of the conduits,dislodging the adherent matter and keeping the surface of the withpersistently adherent matter, dislodging it With gradually built uppressure rather than'by a rigid impact blow which is apt'to bedetrimental to the scraper blades as well as to mar the inner surface ofthe chiller pipe.

Scraper blades that are supported by springs, in previously knownmanner, are subject to vibrations which cause chatter, by which is meanta succession of vibratory impulses against the inner surface of thechiller pipeimmediately following the release of the spring upon thedislodgement of a difiicultly removable particle, which succesconduitpolished. Where spiral type blades are used, the conveying function isquite subordinate to the scraping function, inasmuch as the liquid beingtreated is pumped through the chiller. The spiral disposition of theblades is rather for the purpose of meeting the adherent matter at anangle, and thus performing an inclined shearing cut.

Scraper blades are generally of the narrow or ribbon type, and may beeither rigidly or resiliently supportedfrom a driven shaft arrangedcoaxially Within the chiller pipe.

Spring supported blades have the advantage over rigidly supportedblades, for not only can they accommodate themselves to variations inthe diameter of the pipe so as to maintain unbroken contact with thepipe throughout their length, and automatically adjusting themselves tocompensate for wear, but they can be so constructed and arranged as toyield upon making contact sion of vibratory blows tends to flatten orscore or groove-the inner Wall of the chiller pipe, a condition whichpromotes rapid Wear of the scraper blades and the chiller pipe, and byroughening the latter encourages the adhesion of the sedimentary matter,and in general, lowers the heat exchanging efiiciency of the apparatus.This untoward action ordinarily affects spring blade supports of theleaf spring type which vibrate laterally, as well as spring supports ofthe coil type which vibrate only axially.

In the aforementioned parent application of which this is a division, aspring support for scraper blades is claimed, in which the springs areof the leaf type, yielding laterally to the resistance of adherentmatter, in which the undesired vibrations are quenched by causing thesprings to bend about a shifting fulcrum as they are laterally stressed,changing their amplitude of vibration and thus quickly bringing them torest..

In said parent application, a hypothetical construction is described andthe defect of such construction pointed out, in which the scraper bladeswould be supported by coil springs at diametrically opposite points,thrusting against the inner wall of the chiller pipe with the entireforce of the springs so that upon meeting an adherent obstruction theywould either forcibly dislodge the obstruction, or if the obstructionhas a sloping side; which is more frequently the case, the blade wouldrise upon said obstruction, pushing inwardly against the spring, andupon passing the obstruction would immediately fly out, deliverin ahammer blow against the surface of the pipe. This blow, if analyzed byan oscillograph, would show as a single major impulse followed by aplurality of lesser impulses, and it can readily be appreciated thatsuch a blow frequently repeated. would destroy the smooth and polishedinterior surface of the chiller pipe.

The present invention has for its object the provision of a spring typescraper blade support, making use of coil springs, but so positionedWith of which the same characters of ing the principles of which in .maybe the chiller pipes I may be quite long, it is custo slight deviationsof posite points the respect to the axis of rotation of the scraperblade unit as to substantially eliminate the harmful impact blow whichthe above hypothetical exthe following description of a preferred andpracj-y,.

tical embodiment thereof proceeds. In the drawing throughout the severalfigures reference have been employed to designate identical parts:

Figure l is a longitudinal view in elevation, showing a portion of theshaft of a scraper blade unit, embodying a spring blade supportembracthe present invention; and Figure 2'is a cross-section through oneof the spring supports, showing also fining the refrigerant jacket.Referring now in detail to the several figures, the reference characterI represents the inner conduit or chiller pipe, 2 being .an outer casingdefining with the chiller pipe ,1 ajacket. 3 in which a refrigerant is.designed to flow.

l The liquid to be chilled, which is frequently: a hydrocarbon oil, ispumped through the chiller pipe I. Extending axially through saidchiller pipe is the shaft 4. The shaft 4 carries the scraper blades 5'and 6.. It will be observed from Figure 2 that the scraper blades 5 and6 are each slidably fitted within slots l8 and I9 formed in the oppositewalls of 8-. 'Said sockets are turn is suitably The scraper blades 5 andoutwardly by means of coil springs i0 and II housed within said sockets,the springs thrusting against followers I2 and i3 against which theinner edges'of the blades 5 and B abut. As a means forpreventing thesprings from flying out and displacing the blades ets when the scraperunit fixedly attached to a hub 9, fixed to the shaft 4'.

is withdrawnfrom the chiller tube, retaining pins 14 and 15 areprovided, which have their ends fixed in the opposite walls of thesockets and tions passing through slots is and I1 formed in the blades.

It will be observed in Figure 1 that the blades 5 and 6 are springsupported at several points. The blades, together with considered ablade unit. Inasmuch as tomary to provide the shaft 4 with several bladeunits arranged end to end, and sometimes in staggered relation. unitspermits them to accommodate themselves alignment, which is apt ofgreatlength. I ,The'salient feature of this invention is the fact thatthe spring blade supports are not in opposite diametrical arrangement,butthat they are offset from the axis of rotation of the unit. It hasbeen already explained that if these coil spring supported to occur inchiller pipes blades would touch theinner surface of the chiller pipe ata point or points substantially normal to the direction of thrust of thesprings.

which they cannot ride, therev is no other out-z come but thattheobstruction must give way.

the outer tube, de- 7 6 are continually urged entirely from the socktheir intermediate ,por-

the spring supports,

The separateness of the the shaft 4 from axialblades wereatdiametrically op- Under such circumstances, if the blades in theirrotation strike an obstruction over 1 first place, the scraper blade nowbecomes a chisel having an acute angled edge on the approach side of theobstruction. This means that the blade will dig into the base of theobstructi'on and, in most instances, remove it.

the respective sockets 'l and However, should the obstruction be soobstinate and so thin at its base as to permit the blade to ride up onit, the blade upon leaving the obstruction, will always be descendingthe sloping wall of the chiller pipe, and therefore, the force of theblow which it will strike against the inner wall of the chiller pipewill be materially reduced almost to the point of elimination. Anotherway of stating, this is that the thrust of the spring will be resolvedinto two components, one which is directed normally to the interiorsurface of the chiller pipe, and the other of which is directedcircumferentially thereof. It is this circumferential component which isentirely lacking in the hypothetical case where the two spring supportblades are positioned at diametrically opposite points.

It will be understood to those skilled in the art that one of theadvantages of the type of spring blade support disclosed in the presentapplication over that forming the subjectmatter of the claims in thehereinbefore parent application, is that in'the former, if one of thepoints of spring support is retarded by an obstinate adherent particle,while the others are free, this causes a twisting of the blades whichreduces the diameter of the scraper in the zone of the point ofretardation, drawing it away temporarily from contact with the surfaceof the chiller pipe. This cannot occur in the present construction, forthere is no lateral deflection of the blades possible, and therefore, nosuch retardation of the movement of the blades as could occur with theleaf type spring support.

While there has been described in the above disclosure what is believedto be a preferred and practical embodiment of the invention, it will beunderstood to those skilled in the art that the details of constructionand the arrangement of parts may be modified to suit the-exigencies ofuse without departing from the spirit and scope of the invention whichis defined in the appended claims.

; What is claimed is:

1. Rotary scraper for the liquid carrying conduits of heat exchangerscomprising a shaft, a ribbon, blade extending longitudinally of saidshaft and, spaced therefrom having a chisel edge adapted to scrape theinner cylindrical surface of the conduit in which said shaft is axiallyinserted, blade supports fixed to said shaft at spaced longitudinalintervals, each support comcarried by said hub having a spring receivingsocket offset from the axis of said shaft with the axis of said sockettangential to an imaginary circle concentric with the axis of saidshaft, said housing having a slot at one end slidably receiving saidblade permitting movement thereof longitudinally of said socket butinhibiting lateral deflection of said blade, and a spring in saidsocket. thrusting against said blade biasing it against the surface ofsaid conduit.

2. Rotary scraper for the liquid carrying conduits of heat exchangerscomprising a shaft, a ribbon blade extending longitudinally of saidshaft and spaced therefrom having a chisel edge adapted to scrape theinner cylindrical surface of the conduit in which said shaft is axiallyinserted, blade supports fixed to said shaft at spaced longitudinalintervals, each support comprising a hub, a spring housing carried bysaid hub having a socket offset from the axis of said shaft with theaXis of said socket tangential to an imaginary circle concentric withthe axis of said shaft, said housing having a slot at one endintersecting said socket and slidably receiving said blade permittingmovement thereoflongitudinally of said socket but inhibiting lateraldeflection of said blade, a coil spring in said socket thrusting againstsaid blade biasing it against the surface of said conduit and a pinintersecting said socket fixed in the walls thereof passing through aslot in said blade for retaining said blade and said spring in saidsocket when the scraper is removed from said conduit.

3. Rotary scraper for the liquid carrying conduits of heat exchangerscomprising a shaft, hubs fixed to said shaft at longitudinally spacedintervals, a pair of spring housings carried by each hub offset from theaxis of said shaft and having spring receiving sockets tangential to animaginary circle concentric with the axis of said shaft, a slot at oneend of each socket, a pair of blades slidably fitting said slots, freelymovable longitudinally therein but restrained thereby from lateraldeflection, coil springs in said sockets thrusting against said bladesbiasing them against the surface of said conduit, said sockets, springsand blades being arranged sym-' metrical with respect to said shaft onopposite sides thereof and in reverse phase.

EMMA BARTMAN VOGEL, Executria: of the Estate 0 Werner G. Vogel,

Deceased.

